August 28, 2002
Mr. Rodney A. Boyd
Trinity Highway Safety Products Division
Dallas, Texas 75356-9619
Dear Mr. Boyd:
Mr. Don Johnsons July 5 letter to Mr. Richard Powers of my staff requested the Federal Highway Administrations (FHWA) formal concurrence that raising the original King offset block 2 inches or 4 inches above the top of the steel support posts would not change the Test Level 3 status of the w-beam rail. He also requested acceptance of a modified block with an open face design for standard use and with the same height adjustment options.
It remains the FHWAs position that a height adjustment up to 4 inches is not likely to change a barriers crash performance, but two bolts must be used for the maximum 4-inch adjustment - one through the rail and block and a second one (to the left or right of the first) through the block alone. The double-bolt attachment is deemed necessary to hold the block in place during a typical impact.
Regarding your request to modify the original design by eliminating the solid face, I agree that this modified block may be used in its normal position (flush with the top of the post), but a full-scale test would be needed for any height adjustment to this design. A pendulum test is not considered a reasonable surrogate for a full-scale test for the combination of a narrow, non-solid block installed above the top of the post because it does not replicate the post bending and twisting that occurs in an actual crash.
(original signed by Carol H. Jacoby)
Carol H. Jacoby, P.E.
Director, Office of Safety Design